The present invention relates to medical devices in general, and in particular to catheter ablation systems for revascularizing occluded vessels.
One common form of vascular disease is characterized by deposits that form in a patient""s arteries or veins. Once such blockages form in cardiac arteries, they are a significant factor in the occurrence of heart attacks.
In addition to cardiac bypass surgery, new less-invasive techniques such as balloon angioplasty or rotational ablation are being used to treat occluded vessels. In the case of rotational atherectomy, a high speed abrasive burr is routed through the patient""s vasculature to the point of the occlusion and used to bore a new lumen through the occlusion in order to restore blood flow. The success of balloon angioplasty and rotational ablation often depends on the nature of the material blocking the vessel. These techniques generally work best when the material is not highly calcified or does not completely occlude the vessel. Total chronic occlusions are typically characterized by a hard calcified material that completely seals off blood flow in a vessel. Some success has been achieved in treating these blockages by advancing a flexible guidewire to the point of the occlusion and xe2x80x9cpeckingxe2x80x9d at the occlusion to create a pathway through it. The problem with the guidewire technique is that it is time-consuming and presents a risk of vessel perforation if the guidewire becomes misaligned.
Given the fact that total chronic occlusions account for between 20-25% of all occlusions treated, there is a need for a system that employs a more aggressive ablation mechanism to reduce the treatment time but reduces the likelihood that the ablation mechanism will become misaligned in the patient""s vessel in order to provide an effective method of treating this type of vessel blockage.
To treat total chronic occlusions, the present invention is a combination ultrasound and ablation catheter that provides a physician with an image of the position of the catheter in the vessel and an image of the occluding material. An ultrasound transducer is located at the distal end of a catheter which generates ultrasound signals and receives corresponding echo signals from the tissue. The echo signals are transmitted to an ultrasound processor which produces an image of the vessel. The catheter is rotated by a driveshaft in order to provide a 360xc2x0 view of the vessel. In one embodiment of the invention, the ultrasound transducer in the catheter is set at an angle such that echo signals are received from a position slightly ahead of the distal end of the catheter.
To create a new lumen in the vessel, radio frequency (RF) ablation energy is transmitted to an electrode that is located at a distal tip of the combination catheter. The RF energy ablates a portion of the occluding material to create a new lumen in the vessel. In one embodiment of the invention, the ultrasound transducer is rotated by a conductive driveshaft. The electrode is electrically coupled to the driveshaft and the RF energy is applied to the driveshaft to be transmitted to the occlusion The conductive driveshaft is surrounded by a non-conductive sheath. The electrode extends out the distal end of the non-conductive sheath such that RF ablation energy is directed from the exposed electrode and into the occluding material.
According to another aspect of the present invention, the electrode at the distal end of the ultrasound catheter may have a variety of shapes including a concave shape, a convex, hemispherical shape with a roughened outer surface or an expandable tip made of a series of braided wires.
In another embodiment of the invention, the catheter system includes an ultrasound catheter having an ultrasound transducer that is rotated by a driveshaft to obtain images of the vessel and occluding material. The ultrasound catheter is routed in one lumen of a multi-lumen catheter. In another lumen of the multi-lumen catheter is a conductive guidewire. RF ablation energy is applied to the conductive guidewire to ablate the occluding material in the vessel.
In accordance with yet another aspect of the invention, the combination ultrasound and RF ablation catheter is routed through a steerable sheath in order to further aid in the placement of the catheter within the vessel. Alternatively, the electrode that delivers the RF ablation energy is incorporated into the steerable sheath, wherein the ultrasound catheter extends through a hole in the electrode at the distal end of the sheath to obtain images of the vessel and occluding material.